Platinum coated molybdenum grid having an intermediate layer of nickel



Aug. 10, 1965 M. A. M. BAKK PLATINUM COATED MOLY INTERMEDIATE Filed Ma ER ET BDENUM GRID HAVING AN LAYER OF NICKEL MARTINUS A-M. BAKKER. JOHANNES CH. DURAN.

BY I M ie e K United States Patent The invention relates to a method of coating by electro-deposition a grid manufactured from molybdenum for electric discharge tubes so that during the whole life of the tube the platinum layer adheres satisfactorily and remains completely intact.

It is known that a lar importance in transmitting tubes in which the grids often assume a very high temperature.

When a grid consisting of molybdenum wire in its definite shape is coated by electro-deposition with a platinum layer without using further means, it is found that this layer at a suflicient strength disengages during operation of the discharge tube and finally surrounds the molybdenum wire like a rolled down stocking.

It is known to manufacture grids from an Mo-Wire which is previously surrounded by a Pt-cylinder and, after heating in a furnace to 135 0 C. is rolled or stretched in a reducing atmosphere to form a thin wire. If desired, the molybdenum core wire with a nickel layer so that it is adapted to slide with accurate fit in a Pt-cylinder. The intermediate nickel layer then serves as solder for the platinum outer layer.

It is found that grids manufactured from such platinum-coated wire are subjected to deformation and warping during operation, in which event even breakage of the wires may occur.

It is known that it is not possible to coat a molybdenum grid which has already obtained its Such a rough intermediate layer may be obtained by applying the metal in the form of oxide which is reduced by heating in a reducing atmosphere.

Now it is found that, as a result of the rough structure of the mtermediate layer, the above-mentioned difiiculties layer which is Consequently heating and during operation, the attachment is further improved by relative diffusion of the metals. Now it is found that the platinum layer does not burst during manufacture, while by appropriate choice of the thicknesses of fixed. During subsequent the intermediate layer and of the platinum layer the time required for the difiusion of molybdenum from the core to the platinum surface is longer than the life (5000 hours) of the tube in which the grid is used, even at an operational temperature of about 1200 C. Owing to the initially obtained mechanical anchorage of the platinum layer, the latter adheres to the substratum during the whole life of the tube. The diffusion of platinum in the core also proceeds so slowly that, when use is made of Consequently, of the grid are maintained.

The intermediate layer may be applied by immersing the molybdenum grid in a suspension of, for example nickel oxide, by drying and heating in a reducing atmosphere until the oxide is reduced to nickel.

layer of, 10 microns and heated during a few hours at 1200 to 1500 C. If the weight of the intermediate layer does not ration of this layer occurs during operation of the discharge tube. A thickness of 0.1;]. has proved to be very favorable. If desired, the intermediate layer may also be provided by electro-deposition and roughened by sandblasting.

Furthermore, it is found that the intermediate layer the platinum layer as a result of the difference between of platinum and molybdenum.

The invention will now be described more fully with reference to the drawing, in which:

FIG. 1 shows a grid according to the invention, and

FIG. 2 is a sectional view of a grid wire.

FIG. 1 shows a grid for transmitting tubes which coninterrnediate nickel layer 4 of 0.1 1"

What is claimed is: 1. A grid for an a thickness of about 5 to 10 and an intermediate layer of nickel firmly bonding said outer platinum layer to said base, said nickel layer having a thickness of about 0.1,u.

References Cited by the Examiner UNITED STATES PATENTS GEORGE N. WESTBY, Primary Examiner. RALPH G. NILSON, Examiner. 

1. A GRID FOR AN ELECTRIC DISCHARGE TUBE COMPRISING A BASE OF MOLYBDENUM, AN OUTER LAYER OF PLATINUM, AND AN INTERMEDIATE LAYER OF A METAL SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, AND NICKEL FIRMLY BONDING SAID PLATINUM LAYER TO SAID BASE, SAID INTERMEDIATE LAYER HAVING A THICKNESS LESS THAN HALF THAT OF THE PLATINUM LAYER. 